Self-checking condition responsive system



A118'- 4, 1964 n. l.. GRAVES ETAL 3,143,162

SELF-CHECKING CONDITION RESPONSIVE SYSTEM Filed April 2e, 1965 MAJOR CYCLE United States Patent O 3,143,162 SELF-CHECKING CONDITIN RESPONSIVE SYSTEM This invention relates to control apparatus and more particularly to condition responsive apparatus such as those useful in supervising fuel burning systems, and to means for insuring reliable operation of the sensory and signal modifying portions of such apparatus.

In condition responsive systems, as for example those used for supervision of combustion established in a furnace chamber, it is desirable that the system react very quickly to the presence or absence of a llame so that excessive amounts of unburned fuel will not accumulate in the chamber in the absence of flame. Electronic llame sensing systems have the desirable rapid reaction to presence or absence of llame, but such systems are susceptible to malfunctions such as, for example, a continuously avalanching sensor of the gas-discharge type which falsely indicates llame presence or a runaway transistor` which continuously passes substantial current to a flame responsive device in the absence of the flame signal normally required to initiate and sustain such current flow. Should such a failure occur, it would be an unsafe type as the sensing system would, in the event of flame failure, continue to react as if llame were present and would therefore permit continued fuel introduction. ln such a case the chamber can accumulate an excessive charge of fuel or fuel vapor which might be ignited explosively by the hot refractory or upon an attempt to reignite the burner. If the sensing system through component failure erroneously indicates the absence of flame, however, fuel introductionl will be terminated and the failure is of a safe type.

In order to check the integrity of such condition responsive systems, it has been proposed to employ a condition absence simulator which operates repetitively at intervals shorter than the deactuation time of the load control device. Failure of the condition responsive device to react properly to the simulated condition absence results in deactivation of the controlled loads. A maj-or disadvantage of this system is the limited life of those mechanical portions thereof which, because of the rapid repetition rate, amass a large number of operations within a relatively short period of time.

Another proposal has been to utilize a timing motor to periodically initiate a condition absence simulation, with the interval between such simulations being appreciably longer than the response time of the load control device. Whereas the less frequent operation of the checking apparatus contributes to its longer life expectancy, there is no assurance against malfunctions of the checking apparatus itself, and when such occur there is no continuing check on the integrity of the condition responsive system.

Accordingly, it is an object of this invention to provide novel and improved control apparatus for checking condition responsive systems.

Another object of the invention is to provide novel and improved control apparatus for use with condition responsive systems which incorporate means to periodically simulate the absence of the condition being sensed and means to check the continued operation of the condition absence simulator.

Another object of the invention sto provide novel and improved load control means in condition responsive systems.

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A further object of the invention is to provide a comprehensive condition responsive system in which the load energization responds to both the condition sensing circuitry and to the checking circuitry so that improved selfchecking operation of the system results.

Still another object of the invention is to provide a novel and improved combustion supervision system of the self-checking type.

In accordance with the invention there is provided a condition responsive system which includes a condition sensor, a condition indicating device and a simulator in which the state of energization of a load device is indicative of the presence or absence of the condition being sensed. However, the energization of the loadrdevice is controlled directly by system checking means and only indirectly by the condition sensor itself. The checking device aslo operates the simulator at regulated intervals to check the operability of the condition sensor and associated circuitry. Coupling is provided between the checking means and the load device which continuously monitors the operability of the checking means so that impaired operation or failure thereof results in de-energization of the load device in the system delay time. In the preferred embodiment the checking means is a cyclically operating timing device which has a major cycle of operation consisting of a plurality of minor cycles, with the duration of each minor cycle being comparable to the system time delay. The coupling circuitry includes two energy storage elements and the application of energy tothe storage elements is controlled in response to the minor cycle signals from the checking device.

vEach major cycle signal operates the simulator to check the operation of the condition sensor and its associated circuitry. Energization of the load device is maintained by the coupling circuitry and malfunction of the checking means, detection of malfunction of the sensing system, or condition failure shuts down both the sensing system and the load device in a safe condition. The condition responsive system of the invention has particular advantage in combustion control systems.

Other objects, features and advantages of the invention will be seen as the following description of a preferred embodiment thereof progresses, in conjunction with the drawing, in which:

FIG. 1 is a schematic diagram of a condition responsive system particularly adapted for use in a combustion control system constructed in accordance with the invention; and

FIG. 2 is a timing diagram indicating the operating sequence of components of the system shown in FIG. 1.

With reference to FIG. l, the circuitry is supplied by a suitable power source such as a volt 60 cycle supply which is connected across terminals 10, 12. This circuitry through contacts 141 and 16-1 supply power to line 18 of the condition sensing circuitry which in the preferred embodiment senses llame supplied by the burner element in a furnace. The condition source (flame) indicated generally as the element 20 is connected between lines 18, 22. It will be understood, of course, that the condition source may exist independently of the condition responsive system power supply. Also connected across the lines 18, 22 is a condition sensor 24 which includes in series a rectifier 26 and a condition indicating device, the coil 28 of the llame relay. Capacitor 30 connected across coil 28 has sufficient energy storage to hold the relay in during the power supply half cycles where power is not supplied to the coil and prevents chattering of the relay contacts. Also included in the condition sensing circuitry is a simulator which in this embodiment includes a shutter 32 operated by a shutter coil 34. When the coil 34 is energized, they shutter 32 is interposed between the condition source 1S and sensor 24 to'simulate the'absence of name for example. The simulator coil 34 is energized when the contact 40, connected in series with it, is closed with contact 39.

Those contacts are controlled by the checking means including timer motor 36. The contacts 39, 40 are closed briefly by single 'crest cam 38 once 4every rotation of the timer shaft 37,- which rotation is termed herein a major cycle. A second set of contacts 39, 41 are normally closed and open only when contacts 39, 40 close as` indicated in FIG. 2. Connected across contacts 39, 41 is `a normally closed `arne'relay contact 28-1.

Also vmounted on the shaft 37 of the timer motor 36 is a multicrest cam 42 which engages a contact 43 to move that Contact between contacts '44 and 46. Each complete cycle of contact'43 is termed herein a minor cycle. Contact 43 is connected to line 18 through resistor 48, rectifier 50 'and normally open contacts 28-2 of the ilamerelay. As the timer shaft 37 rotates, the contact 43 is moved back and forth between the contacts 44 and 46 in a minor cycle operation so that contacts 44 and 46 are alternately connected to line 18.

This operation applies energy to the checking means coupling circuitry which includes two relay coils 14, 16, each of which has an energy storage capacitor 52 connected across it which provides a relay drop out delay after de-ener'gization of the relay coil equal to the system time delay, which in the lcombustion control system of the preferred embodiment is approximately three seconds. 1nv addition to the' main control contacts 14-1, 16-1 which energize the checking means and the condition senso-r circuitry, there are normally closed contacts 14-2 and 16-2 which are connected in series with the opposite relay coil;and normally open contacts 14-3 and 16-3 which are connected-in series between the minor cycle contacts 44, 46 and their own relay coils. The main control contacts 14-1, 16-1 are connected in series with `a'ncl directly control the energization of the load-54, which in a combustion control system typically includes a fuel valve.

A circuit controlling push button structure 56 has a set of normally open contacts 56-1 and a set of normally closed contacts 56-2. Contacts 56-1 are connected to terminal and through diode 58 and resistor 60 to the checking means coupling circuitry, while contacts 56-2 are connected between terminal 10 and the main control contacts 14i-1, 16-1.

In operation, with power applied at terminals 10 and 12, upon depression of push button 56, contacts 56-2 are opened and contacts 56-1 'are closed. When contacts 56-1 close, power is supplied through diode 58 and the normally closed contacts 14-2 and 16-2 to energize the rcoupling circuitry relays 14 and 16. With this energization, the contacts 14-1 and 16-1 close, and with the release ofl pushbutton 56, contacts 56-2 close and the load 54 is energized. At the same time power is supplied to the condition sensor 24 and the timer motor 36. As soon as the condition sensor 24 detects the condition from the source, relay 28 is energized to close contacts 28-2 and energize contact '43. The timer motor drives the minor cycle cam element 42 to move the contact member 43 between contacts 44 and 46.

Power'is Vsupplied alternately through the contacts 44 and 46 and the closed contacts 14-3 and 16-3 to recharge the capacitors 52 associated with the coupling circuitry coils 14 and 16. Thus, the checking' cam 42 connects eachrelay in circuit regularly within a period less than the system delay time (the drop out time of either relay 14 or 16) and each capacitor 52. is recharged so that the main control contacts 14-1, 16-1 will remain in their closed position holding the load 54 energized. 'Should the timing motor slow down or stop, such that one relay capacitor 52 is not recharged with the system delay time, the associated relay will drop out and the mainV circuit load controlling contacts 14-1 and/ or 161 will open, de-energizing the load 54. At the same time the remainder of the circuit will also be cle-energized in an automatic manner. It will be noted that this response occurs within the period of a minor cycle upon occurrence of a checking means malfunction.

Should the condition sensor 24 not detect the presence of the condition being sensed at any time, relay 28 will drop out substantially immediately and open contacts 28-2 which will de-energize the coupling circuitry independently of the operation of the timing motor 36 and causev one coupling relay 14 or 16 to drop out within the predetermined system delay time to open the main control contacts 14-1 and 16-1 and fle-energize the load.

At the end of each major cycle contacts 39, 46 close at substantially the same time that contacts 39, 41 open. Timing motor 36 stops and shutter solenoid 34 is energized to position shutter 34 between condition source 20 and sensor 24 simulating absence of the sensed condition. Relay 28 drops out promptly if the condition sensing circuitry is operating properly.` That drop out closes contact 28-1 and restarts 'timing motor 36. 'vWith that restart, contacts 39, 40 are opened, de-e'nergizin'g the shutter solenoid 34 and removing the shutter 32 from between the source 2l) and sensor 24 so that the relay 2S again is energized to reclose contacts 2842 and open contacts 28-1, thus initiating another major cycle and restoring the coupling circuitry to its energized state. Should the condition indicating relay 28 fail to drop out, however, the timing motor 36 will not be restarted and the coupling circuitry will remain de-ene'rgized as contacts 2842 are held open s'o that the main control contacts 14-1 and 16-17open within the system time 'delay to de-energize the load 54. y

Thus it will be vseen that the invention provides a novel and improved condition responsive system in which the energization of the load devices is controlled directly by system checking means through a coupling circuit arrangement. The coupling circuit continuously monitors the operability of the system checking means. Should there be a substantial malfunction of either the sensing system or the checking means or any of their components, the coupling circuit de-energizes the load within the system time delay. Also should a coupling circuit component fail, the load will also be de-energized to place the supervised system in safe condition. Should diode 50 fail, for example, either alternating voltage will be applied to the relays so that the capacitors 52 will not accumulate charge or no voltage will be applied to those capacitors. Should either capacitor 52 fail open, there will be no delay in drop out of its relay and should it short, the relay coil cannot be energized. Thus it will be seen that the invention provides a novel and improved control and checking arrangement for a condition responsive system. While a preferred embodiment of the invention has been shown and described, various modifications therein will be apparent to those yskilled in the art. Therefore, it'isnot intended that the invention be limited to the disclosed embodiment or to details thereof and departures may be made therefrom within the spirit and scope of the invention as defined in the claims.

We claim: 1. A condition responsive ksystem comprising a load device,

cyclically operated checking means for producing a major cycle signal and a plurality of minor cycle signals in each major cycle, each said minor cycle being of shorter duration than said major cycle, couplingmeans responsive to said checking means for controlling the energization of said load device, means to apply said minor cycle signals to said coupling means to energize said load device, a condition sensor, condition indicating means coupled to said sensor for producing a signal indicative of the presence of the condition being sensed,

means responsive to said condition indicating means to disable said coupling means,

simulator means to simulate a condition absence,

and means to apply a major cycle signal from said checking means to operate said simulator means.

2. The system as claimed in claim 1 wherein said coupling means includes energy storage means and said checking means recharges said energy storage means every minor cycle.

3. The system as claimed in claim 1 and further including means responsive to said major cycle signal to de-energize said checking means and means responsive to said condition indicating device to energize said checking means.

4. A condition responsive system comprising a load device,

a timing motor,

means responsive to said timing motor to generate a major cycle signal and a plurality of minor cycle signals between successive major cycle signals, each said minor cycle being of shorter duration than said major cycle,

coupling means controlling the energization of said load device,

means to apply said minor cycle signals to said coupling means to energize said load device,

a condition sensor,

a condition indicating device coupled to said condition sensor for producing a signal indicative of the presence of the condition being sensed,

means to simulate the absence of the condition being sensed,

means to apply said major cycle signals to said simulating means to produce a simulated condition absence and to de-energize said timing motor,

and means responsive to the de-energization of said condition indicating device to disable said coupling means and to re-energize said timing motor.

5. The system as claimed in claim 4 wherein said coupling means includes two energy storage elements and said checking means charges said energy storage elements in succession every minor cycle.

6. A combustion supervisionsystem comprising a llame sensor for disposition in supervising relation to a combustion chamber,

a flame relay coupled to said flame sensor for producing 5 a signal indicative of the presence of flame in said combustion chamber,

control means to cause said flame sensor to indicate ilame failure,

an electrically operable combustion control device,

coupling means controlling the energization of said combustion control device, cyclically operative checking means generating a major cycle signal and a plurality of minor cycle signals within said major cycle, each said minor cycle being of shorter duration than said major cycle,

means to apply said minor cycle signals to said coupling means to energize said combustion control device,

means to apply said major cycle signals to said control means to produce a simulated flame failure condition,

and means responsive to said flame relay to disable said coupling means.

7. The system as claimed in claim 6 wherein said coupling means includes energy storage means and said checking means recharges said energy storage means every minor cycle.

8. The system as claimed in claim 6 wherein said coupling means includes two energy storage elements and said checking means charges said energy storage elements in succession every minor cycle.

9. The system as claimed in claim 6 wherein said checking means comprises a timing motor, a timing motor controlled contact connected in series with said motor and a flame relay contact connected in parallel with said motor.

10. The system as claimed in claim 9 wherein said coupling means includes two slow release relays connected in parallel, each slow release relay controlling a contact connected in series with said load, a llame relay contact connected in series with both slow release relays, and timing motor controlled contacts to apply power to said slow release relays in succession to each minor cycle.

References Cited in the le of this patent UNITED STATES PATENTS 2,084,880 Wotring .Tune 22, 1937 2,763,853 Grant Sept. 18, 1956 2,814,740 Smith Nov. 26, 1957 2,865,444 Deziel Dec. 23, 1958 3,072,177 Fennell Ian. 8, 1963 

6. A COMBUSTION SUPERVISION SYSTEM COMPRISING A FLAME SENSOR FOR DISPOSITION IN SUPERVISING RELATION TO A COMBUSTION CHAMBER, A FLAME RELAY COUPLED TO SAID FLAME SENSOR FOR PRODUCING A SIGNAL INDICATIVE OF THE PRESENCE OF FLAME IN SAID COMBUSTION CHAMBER, CONTROL MEANS TO CAUSE SAID FLAME SENSOR TO INDICATE FLAME FAILURE, AN ELECTRICALLY OPERABLE COMBUSTION CONTROL DEVICE, COUPLING MEANS CONTROLLING THE ENERGIZATION OF SAID COMBUSTION CONTROL DEVICE, CYCLICALLY OPERATIVE CHECKING MEANS GENERATING A MAJOR CYCLE SIGNAL AND A PLURALITY OF MINOR CYCLE SIGNALS WITHIN SAID MAJOR CYCLE, EACH SAID MINOR CYCLE BEING OF SHORTER DURATION THAN SAID MAJOR CYCLE, MEANS TO APPLY SAID MINOR CYCLE SIGNALS TO SAID COUPLING MEANS TO ENERGIZE SAID COMBUSTION CONTROL DEVICE, MEANS TO APPLY SAID MAJOR CYCLE SIGNALS TO SAID CONTROL MEANS TO PRODUCE A SIMULATED FLAME FAILURE CONDITION, AND MEANS RESPONSIVE TO SAID FLAME RELAY TO DISABLE SAID COUPLING MEANS. 